A conventionally known vehicular-wheel bearing assembly (hub unit) to which wheels of an automobile are mounted includes an inner shaft to which a wheel and a brake rotor of a disk brake are mounted, and an outer ring that is fitted to the inner shaft from outside via two rows of rolling elements and is secured to a vehicle body. Raceway surfaces for the rolling elements are formed in two areas in an outer peripheral surface of the inner shaft, an outer peripheral surface of an inner ring member fitted to the inner shaft from outside, and an inner peripheral surface of the outer ring.
The outer ring and the inner shaft are made of, for example, carbon steel material such as S55C (carbon steel material for mechanical structure) by hot forging. Further, the raceway surfaces that require high hardness, and a base of a flange portion to which the wheel is mounted in the inner shaft are subjected to heat treatment (high frequency quenching and tempering). This increases performance and life. Such heat treatment, however, is a factor of increasing production costs. Particularly, selective quenching of the inner peripheral surface of the outer ring and the outer peripheral surface of the inner shaft having complicated shapes is difficult and increases production costs.
Thus, for example, as described in Japanese Patent Laid-Open No. 2003-294031, a configuration is proposed in which an inner shaft is formed by cold forging of a tubular material to reduce an area of cutting or polishing, thereby reducing production costs.
Another known vehicular-wheel bearing assembly to which wheels of an automobile are mounted includes an inner shaft having a flange portion to which a wheel side member is mounted, and an outer ring that is fitted to the inner shaft from outside via two rows of rolling elements and is secured to a vehicle body. The wheel side member includes a wheel and a brake rotor of a disk brake.
For example, as described in Japanese Patent Laid-Open No. 2003-291604, a guide member that serves as a guide for mounting a wheel side member to a mounting surface of a flange portion is provided at an end of an inner shaft. The guide member is a separate member from the inner shaft for simplifying the shape of the inner shaft formed by forging, which facilitates production and reduces costs.